Hi John, 1098 is the reference (type, model) of the bracelet, 540 the reference of the end links. 31 in the circle is an Omega code snd seems to me to be a hint of the production series. I have no proof that e.g. an 11 in a circle means that it is an older execution, but sometimes it looks like, because older bracelets of the same reference have screwed exchangeable links, younger ones have spring loaded exchangeable links,
kind regards, Max